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Did you know that the resolution of a photo is completely irrelevant when you’re using them in a web site design? It’s true. In this unit, we’ll explore such technical facts in depth.

on-screen-resolution

If you open these two images and view them at 100% (by typing ⌘-1), you’ll see they zoom to the same size on screen. That’s because they’re both 1000 pixels wide.

Now go Image > Image Size. Notice how one of them has a resolution of 72dpi and the other has a resolution of 240dpi. Why do they both look the same on screen? If you were to print them, the 240dpi image would look much better.

This tells you that pixel dimensions are relevant on screen and resolution is relevant to print.

As a graphic designer, you’ll be manipulating raster images for many different intents: high-end printing, app design, large format signage, etc… Being aware of the mechanics of what’s happening to the pixels in your images is crucial to successful reproduction.

These are two excellent articles on the topic of resolution and pixel dimensions. The definitive guide to DPI & PPI and Pixel Density Demystified. This is Adobe’s Support page for raster & vector graphics This is a good source of information.

Resampling

Resampling is changing the amount of image data as you change either the pixel dimensions or the resolution of an image. When you downsample (decrease the number of pixels), information is deleted from the image. When you resample up (increase the number of pixels, or upsample), new pixels are added. Adobe

Open this image. It’s named 02-resample-9”x6”.psd.

resample-6'x4'

Go Image > Image Size…

image-size-1

This is a very large image. It measures about 18” wide by 12” tall at 300dpi in print. That makes it weigh in at about 58 megabytes on your hard drive.

Let’s say we want to use it in a page layout in InDesign at 9” wide by 6” tall. All we need to do is enter 9” for the width while Resample is checked.

image-size-2

Notice the following:

  • The image’s size on disk goes from 58.8MB to 13.9MB. Proof that we’re removing data.
  • The Height & Width values should always remain locked to avoid distorting the image.
  • The Resample checkbox is checked. This means we’re removing pixels, so this is destructive.

The operation we’re performing here is resampling. This means that we’re removing pixels from the image, which is a destructive process. If you were to save and close this image, that data would be lost forever.

If we place the image on a page in InDesign at 100%, it will print at 9” wide at 300dpi, which is what we want.

Resizing

When you resize an image and do not resample it, you change the image’s size without changing the amount of data in that image. Resizing without resampling changes the image’s physical size without changing the pixel dimensions in the image. No data is added to or removed from the image. Adobe

If I wanted to use a raster image on a large format banner to hang on a building wall, I would want the dimensions to be large. The resolution for printing on vinyl can be much lower. Our sign company tells us it can be as low as 100dpi.

Let’s resize image 03-resize-100dpi.psd as big as we can get it at 100dpi. Uncheck the Resample box. Enter a value of 100 for the resolution. This will cause the dimensions to increase from 19” wide to 57” wide.

resize-100dpi

Notice the following:

  • The image size remains unchanged.
  • The Resample checkbox is unchecked, which means we’re resizing.
  • The Height, Width and the Resolution values become linked when the Resample checkbox is unchecked.

The operation we’re performing here is resizing This means that we’re not changing the number of pixels in the file. The file size on disk remains the same at 63.3 megabytes. This is a non-destructive process. You can resize images up and down to your heart’s content. You’ll never lose data.

Placing an Image

When you place an image on a page in an InDesign document, there’s a link to the original file on your hard drive. What you’re seeing is a picture of the image in InDesign. InDesign’s command for importing a graphic onto a page is called Place rather than import.

In InDesign (as in Illustrator) to get a raster image onto a page, you need to use the File > Place… command.

indesign-placing-images-command

Once you do so, you should click and drag to size the photo to the dimensions you want.

If you wish to place a series of images at once, you can use the File > Place… command, then choose multiple images. Once you do so, you’ll get a cursor loaded with all the images. Then, you can click and drag them onto your pages one after the other.

Resizing Images in InDesign

When a graphic or a photo is placed on the page in InDesign, it’s a image inside and InDesign frame. The brown frame is the graphic itself. The blue one is the InDesign frame which contains it.

indesign-image-frame

You usually want to resize the frame containing the image after you’ve placed it. To do so, grab a corner of the InDesign frame with your Selection Tool.

  • Hold only Shift to scale the InDesign frame, but not the image.
  • Hold ⌘-Shift and drag to scale the frame and the image.
  • Hold Option-⌘-Shift to scale the frame and the image from the center.

When you select an image in InDesign, a circle appears at its center. This is called the Content Grabber. It allows you to drag the image around inside the InDesign frame. This can be useful for cropping an image inside the frame.

The Links panel lists all the images you’ve placed in your document. There’s a tonne of information in the lower part of the panel about each image.

indesign-links-panel

It’s important to keep image files well organized in your project folder because InDesign will reference that location to find the linked files. If you rename or move an image in Finder after its been placed, InDesign will lose track of the image.

What Does 100% Mean?

When we place raster images in InDesign, it’s fine to resize them at will while we’re designing our document. When our design is completed, you should resize your images to 100% before sending files for reproduction. The 100% means that the print size in Photoshop matches the print size in InDesign.

Let’s see what that process looks like. Create a new default InDesign document. Just one page. Place the 04-100-percent.psd image on the full width of the margins.

indesign-placed-image

Click on the content grabber, then check the Control Bar’s size value to see what’s going on. You can see that it’s scaled to about 9.5% in InDesign. We need to make this number 100%, with the image resolution at 300dpi.

100-percent-step-1

Open the placed image in Photoshop, then go Image > Image Size…. If we uncheck Resample, then set the resolution to 300, the dimensions go down. Let’s save, leave the image open, then switch to InDesign.

100-percent-step-1

When we switch to InDesign, it’s now reporting that the image is placed at about 40%. Let’s go back to Photoshop to resample to image to 40% of its size.

100-percent-step-1

Make sure that Resample is checked. Switch the units of measure to Percent. Enter a value of 40. You see that the image size went from 60.7 megabytes to 9.71 megabytes. Again, resampling is a destructive process.

Let’s save the image, leave it open and return to InDesign.

100-percent-step-4

You can see that the image is at 100%. Our photo now prints the same size in InDesign as it does in Photoshop. This is our goal.

Low-Rez Images for Print?

I’m sure you’ve heard before that it’s not possible to use an image from the web in print; that you can’t use a 72dpi image in print. That’s not completely true. If an image’s pixel dimensions are large enough, you can use that to get a higher resolution.

This is like taking a really large sand box with very little sand in it, then shrinking in its walls towards the center. As the sand box gets smaller, the sand will get deeper. The deeper sand is a metaphore for higher resolution.

Let’s open 04-resize web to print.psd. In the Image Size dialogue, you see that it’s a huge image. If you were to print it as-is, it would measure 80 inches wide. The quality wouldn’t be so great because of the 72dpi resolution.

resize-resample-72dpi

Our goal is to get this image to print 9” wide at 300dpi. The first step is to resize the image, so uncheck the Resample checkbox. Set the resolution to 300dpi. Now check the Resample checkbox again to resample the image dimensions to 9” wide.

resize-resample-web-to-print

In the second dialogue, you can see that the image went from 63.3 megabytes to 13.9 megabytes. Clearly, data was removed from the image when we resampled it. That’s what downsampling is.

So we’ve successfully taken a 72dpi image and made safe for high-quality print output at 9” wide at 300dpi.

Formative Activity

Resampling

exercise-resample

Resample the first image to 9” wide by 6” tall.

Resizing

exercise-resize

Resize the image to be 300dpi.

Place at 100%

exercise-100-percent

Place the image on a letter landscape InDesign page at 9” wide by 6” tall at 300dpi.